第二次世界大戰之後，日本接受戰敗事實，由盟軍進行佔領日本，先後完成簽訂舊金山和平條約、修訂日本國憲法及日美安全保障條約，並於盟軍退出後，日本恢復主權，構築維護日本主要安全之保障體制，使日本在無後顧之憂之有利條件下，維持六十五年之和平，讓日本得以全力發展經濟，成為經濟大國。 然而隨著國際情勢發展，日本亟欲走出經濟大國、政治小國之窘境，然而卻因為在安保體制下，日本憲法第九條與日美安保條約規範內容形成法與政治對立之狀態，引發違憲爭議與自衛隊合法性等問題，致使日本國內存在憲法與條約何者為優位之爭論；其後更影響日本自衛隊雖然參與聯合國維和行動之規模與形式，惟仍無法獲得國際社會與日本民眾的多數認同。尤其是日本民眾普遍雖贊成自衛隊參與國際救災及人道救援等行動，但對於其他更積極之維和行動則傾向於維持現行規模，不宜更積極參與，以免觸及修憲及捲入戰爭等嚴肅議題。因此，近期雖積極尋求修憲解決，但由於日本國內對於修憲尚無法取得多數共識，短期之內恐怕無法如願以償。 本論文的研究架構共分為五章。第一章是緒論，就本論文之研究動機與研究目的、研究範圍與研究方法做整體性的說明。第二章以日美安全保障體系之形成與結構作一簡述，並對日美安保條約與日美行政協定之內容加以說明。第三章以日本安全保障政策之形成過程，就已掌握之第一手歷史資料做基本性質分析，以瞭解日本對於國家安全保障政策之研擬及其形成過程。第四章針對日本安全保障政策之變遷及影響，就日美防衛合作體制之形成，加以說明後冷戰時期日美同盟之新趨勢。第五章日本戰後安全保障政策與變遷之回顧與展望。本章係就已掌握之第一手歷史資料，回顧並整理、探討日本戰後其安全保障政策之形成與變遷，期能獲致瞭解日本如何恢復國格與邁向正常化國家之脈絡並對日本擬修改憲法及成立國防軍等情事，予以觀察。Japan accepted its defeat and the Allied occupation after World War II, and it signed the Treaty of San Francisco, amended its Constitution, and also signed the Treaty of Mutual Cooperation and Security between the United States and Japan, respectively. These covenants constituted the primary security system for upholding Japan’s safety after the Allied withdrawal and the restoration of Japanese sovereignty. With no security threat to worry about, Japan used this advantage cunningly and was able to maintain peace for 65 years, during which time it focused on developing its economy, and ultimately became a major economic power. Nevertheless, with the progression of the international situation, Japan faced numerous obstacles as it fought actively against being a major economic power yet a weak political entity. Under the U.S.-Japan security system, the content in Article 9 of the Japanese Constitution and the Treaty of Mutual Cooperation and Security between the United States and Japan resulted in conflict between law and politics, and it further raised questions as to the constitutionality, legitimacy of the Japan Self-Defense Forces, and supremacy of the Constitution vs. the Treaty. Subsequently, although the Japan Self-Defense Forces participated in the United Nations’ peacekeeping operations in both scale and form, they still had difficulty gaining approval by either the international community or the majority of the Japanese citizens. Specifically, even though most Japanese citizens support the Japan Self-Defense Forces’ involvement with international disaster relief and humanitarian relief operations, they tend to support the status quo in regards to the more aggressive peacekeeping operations in avoidance of serious issues such as amending the Constitution and engaging in wars. Therefore, while some are actively seeking an amendment to the Constitution as a solution, due to the lack of a majority consensus, such goal is unlikely to be realized in the near future. There are five chapters in the thesis. Chapter 1, the introduction, gives an overview of the research motivation, objectives, scope of research, and methodology. Chapter 2 talks briefly about the formation and structure of the Mutual Cooperation and Security between the United States and Japan system, and it also elaborates on the contents of the Treaty of Mutual Cooperation and Security between the United States and Japan and the Administrative Agreement under Article III of the Security Treaty between Japan and the United States of America (February 28, 1952). Chapter 3 analyzes the nature and development of Japan’s national security policy based on known historical materials. Chapter 4 centers on the transformation and effect of Japan’s national security policy. With reference to the formation of the U.S.-Japan Security Alliance, it explains the new trend in the U.S.-Japan Alliance during the post-Cold War era. Chapter 5 discusses the significance of the Treaty of Mutual Cooperation and Security between the United States and Japan based on the U.S.-Japan Security Alliance. It also contemplates issues regarding amendment to the Constitution of Japan, the potential of granting the Japan Self-Defense Forces as much authority as does the Marine Corps in order to “guard” the outlying islands, and raising warning and surveillance efforts via the introduction of unmanned reconnaissance aircraft. Then through the results of the aforesaid discussion, we deduce whether Japan can end the long-standing conflict between its law and politics and enter the operating mode of a normal country. In conclusion, the thesis studies the formation and transformation of Japan’s national security policy post-World War II, and may it be of reference to future scholars.